As disclosed in Japanese Patent Laid-Open Publication No. 2000-68327 for example, a conventional component mounting apparatus utilizing ultrasonic vibration typically includes a mounting head equipped with a horn and a suction nozzle, means for feeding an electronic component to the mounting head, a supporting base that holds the mounting object, and a positioning device that relatively moves the mounting head against the supporting base in the horizontal direction to put the electronic component in the right place on the mounting object. The horn is coupled with the output of an ultrasonic vibration generator horizontally fixed to a supporting bracket that is vertically movably supported by a moving mechanism such as a voice coil motor, while the suction nozzle that holds the electronic component is installed at the end of the horn.
Component mounting apparatuses of this type are suitably employed when a plurality of bump electrodes formed on a face of the electronic component are ultrasonically bonded onto leads formed on the mounting object. The suction nozzle holds the top face of an electronic component that has been fed with its bump electrodes facing down, while the supporting base secures the mounting object thereon. The electronic component is put in the right place on the mounting object by relatively moving the mounting head against the supporting base, and then the bump electrodes of the electronic component are contacted with the leads of the mounting object. With a predetermined pressure load applied on the component, the suction nozzle is vibrated in the horizontal direction via the horn with ultrasonic vibration generated by the ultrasonic vibration generator. The ultrasonic vibration energy is provided to the contact face between the electronic component and the mounting object, and they are bonded by diffusion and melting.
In these years, however, there is a need for reducing the number of electronic components (chips) to downsize electronic circuits, and the functions and density of electronic components have been much improved. As a result, individual electronic components have become larger and come to have more electrodes than ever. For example, electronic components (bare IC chips) were about 0.3 to 5 mm per side and had about 2 to 30 bump electrodes. However, they are expected to be 10–20 mm per side and have 50–100 or even 1000 or more bump electrodes in the near future.
When such an electronic component is mounted on a circuit with a conventional component mounting apparatus, the pressure load applied to the suction nozzle must be large to bond many bump electrodes at a time to the leads of the mounting object by ultrasonic vibration. In addition, the bottom face of the suction nozzle holding the component must be aligned precisely parallel to the bonding face of the mounting object to ensure bonding between all the bump electrodes and the leads of the mounting object. For instance, when mounting such a large bare IC chip, the component holding face of the suction nozzle must be maintained parallel to the bonding face of the mounting object over the entire area within a tolerance of 5 μm in the direction of ultrasonic vibration.
However, in the above configuration, if a large pressure load is applied by the supporting bracket to the vicinity of the junction between the ultrasonic vibration generator and the horn, since the suction nozzle is fastened to the end of the horn, and thus, the bottom face of the suction nozzle is distant from the position receiving such pressure load, a bending moment works on the horn. Then a deformation of the horn due to the pressure load makes the component holding face slant, and a precise parallelism cannot be obtained. Meanwhile, there is an idea to insert an elastic unit between the horn and the component holding face of the suction nozzle for ensuring parallelism therebetween. This, in turn, significantly lowers the ultrasonic vibration propagation efficiency. Then bonding efficiency becomes lower, and reliable bonding cannot be provided.
When the chip has many bump electrodes, the bonding energy provided by ultrasonic vibration is likely to be short, even if the parallelism between the component holding face and the bonding face of the mounting object is maintained and a large pressure load is applied along with ultrasonic vibration. Then it becomes difficult to carry out bonding with high reliability.
There has been another problem that the process cost becomes high because extra steps are needed to fill a seal material in between the chip and the mounting object after bonding and then to thermo-cure the seal material.
On the other hand, there is an ultrasonic bonding head where one end of an oscillator working as the horn is coupled with the output of the ultrasonic vibration generator while the other end has a working face disposed parallel to the bonding face.
According to this method, however, the pressure load must be large to ensure bonding if the bonding area is large or the total bonding area of multiple bump electrodes is large. At the same time, the parallelism between the working face of such a working unit and the bonding face of the mounting object must be kept excellent to ensure bonding over the entire bonding area.
In fact, however, excellent parallelism cannot be provided because a bending moment works on the oscillator when a large pressure load is applied thereto and because the working face slants due to the bend of the oscillator. Particularly when a plurality of bump electrodes are arranged over a wide bonding face, it is difficult to ensure parallelism. Otherwise, if ultrasonic vibration is provided under a pressure load that does not cause such a slanting problem in the working face, the bonding energy of ultrasonic vibration may not be high enough to provide a reliable bonding condition.
An object of the present invention is to provide a component mounting method and apparatus, and an ultrasonic bonding head that ultrasonically bonds components with high reliability even when the component has many bump electrodes, and thus, the bonding area between the component and the mounting object is large.